A known ignition device for use in combustion apparatus, such as an internal combustion engine, includes an ignition coil having a primary coil and a secondary coil; a discharge power supply for applying voltage to the primary coil; and an ignition plug electrically connected to the secondary coil and having a center electrode and a ground electrode with a gap formed between the two electrodes. In such an ignition device, high secondary voltage generated in the secondary coil as a result of application of voltage to the primary coil is applied to the ignition plug, thereby generating spark discharge across the gap; as a result, fuel gas is ignited.
In recent years, in order to further improve ignition performance, there has been proposed a technique for generating spark discharge through supply of AC power (high-frequency power) to the gap from an AC power supply in place of application of high voltage (refer to, for example, Patent Document 1).